Sienna Miller 'Too Angry for Tears'

Amid reports that her engagement to Jude Law could be kaput following his public admission that he had an affair with his children’s nanny, Sienna Miller’s London stage role in As You Like It went to her understudy Tuesday night.

“The As You Like It management has made the decision that at this evening’s performance the role of Celia will be played by Denise Gough,” read a sign that greeted theater patrons and the army of reporters tracking Miller’s movements since Law’s lapse hit headlines.

On Monday, Miller, 23, arrived at the theater without her engagement ring and quickly left after the performance. She is expected to return to work Wednesday.

On Tuesday, however, Miller’s costars remained tight-lipped about how the actress is holding up, though Dominic West (who appeared with Julia Roberts in 2003’s Mona Lisa Smile), tells PEOPLE, “She’s fine.”

Slightly more forthcoming was Miller’s mother, Jo, who spoke to reporters from the door of her home. Saying “Sienna is probably too angry for tears at the moment. It is anger and betrayal,” Jo went on to reveal, “Sienna is not with Jude at the moment. … I can’t comment on whether they will stay together.”

Referring to Sienna as “an absolute trouper,” Mom added: “Never in a million years would I have suspected that he would do that to my daughter.”

Also at the Miller home was a man who would only identify himself as “a family friend who has known Sienna since she was 10.” He said that Sienna is “in a secret location in the country. She’s not in London. She’s in talks with Jude. She’s taken the day away to sort things out.”

As for Law, the friend said: “In my opinion he’s an absolute fool. He’s hurt the family more than he’s hurt Sienna. For that they won’t forgive him, but it’ s what Jude does. He’s good at breaking people’s hearts and mucking people about.”

This week’s Sunday Mirror first reported that Law, 32, and Daisy Wright, a 26-year-old au pair, had a steamy affair in March while Law was filming All the King’s Men in New Orleans.

In a statement that followed the story, Law said: “I am deeply ashamed and upset that I’ve hurt Sienna and the people most close to us. …There is no defense for my actions, which I sincerely regret and I ask that you respect our privacy at this very difficult time.”

A representative for both Law and Miller tells PEOPLE that she has no comment beyond Law’s statement.

According to reports, Law’s ex-wife Sadie Frost hired Wright. Law – named PEOPLE’s Sexiest Man Alive last year – and Frost had been married from 1997 to 2003. They have three children.

Law and Miller, who became engaged last Christmas, met on the set of the 2004 movie Alfie.